The present invention relates to an assembly and a method for creating an expanded tubular element in a borehole. The borehole may extend into an earth formation, for instance for the exploration or production of hydrocarbons.
Wellbores for the production of hydrocarbons are generally provided with steel casings and/or liners to provide stability to the wellbore wall and to prevent uncontrolled flow of fluid between the wellbore and the surrounding earth formation. A casing generally extends from surface into the wellbore, whereas a liner may extend only a lower portion of the wellbore. However in the present description the terms “casing” and “liner” are used interchangeably and without such intended difference.
In a conventional wellbore, the wellbore is drilled in sections whereby each section is drilled using a drill string that has to be lowered into the wellbore through a previously installed casing. In view thereof the wellbore and the subsequent casing sections decrease in diameter with depth. The production zone of the wellbore therefore has a relatively small diameter in comparison to the upper portion of the wellbore. In view thereof it has been proposed to drill a “mono diameter” wellbore whereby the casing or liner to be installed is radially expanded in the wellbore below a previous casing, after lowering to the required depth. Subsequent wellbore sections may than be provided with expandable liners, wherein each liner is expanded to substantially the same inner diameter as the previous liner or casing. If subsequent liner sections are expanded to the same diameter as the previous section, the wellbore inner diameter may remain substantially constant along at least a part of its length.
Subsequent wellbore section may therefore be drilled at a diameter larger than in the conventional wellbore, which may allow the wellbore to have a larger inner diameter at target depth than a conventional wellbore.
US-2006/0065403-A1 discloses an assembly for expanding a tubular element in a wellbore, whereby the tubular element is suspended during running-in into the wellbore on an expansion string having an expander at its downhole end, and whereby the tubular element passes through an existing casing in the wellbore. There is a risk that the lower end of the tubular element is prematurely expanded by the expander, for example if the weight of the tubular element causes the tubular element to slip downward relative to the expansion string and consequently partly expand. Such unintended expansion may hamper, or even prevent, introduction of the tubular element through the existing casing.
US patent application US2009/0139732 discloses a downhole swaging system with an expandable secondary swage, which is expanded if a primary swage encounters an increased resistance to swaging generated by a load ring or a section of increased thickness or strength of the expandable tubular. The known load ring or section of increased resistance are located at a location along the length of the expandable tubular where the secondary swage needs to be expanded and they are not arranged at a lower end or the expandable tubular and do not support the expandable tubular during descend into a borehole prior to the expansion process.
Other downhole well tubular expansion systems are disclosed in US patent applications US2009/139732 and US2012/298379, International patent applications WO2012/104257 and WO2014/151314 and in European patent application EP 1717411.
These known assemblies are not provided with a starter joint. There is a need for an improved assembly for supporting and expanding a expandable tubular wherein the expansion string may be locked to a starter joint during transport to the rig and during make-up of the tubular element on the rig floor, which starter joint transfers the weight of the tubular element to the expansion string without the tubular element being prematurely expanded, and may furthermore transfer rotary torque from the expansion string to the tubular element required for making-up and breaking-out of the on-off sub connection and for reaming with the expansion assembly while running into the borehole and which may also transfer a downward force from the expansion string to the tubular element to enable the tubular element to be pushed into the borehole in case obstructions are encountered on the way down.
It is an object of the invention to provide an improved assembly for lowering and expanding a tubular element in a borehole.